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SubjectRe: [RFC -resend] Make Yama pid_ns aware
Quoting Vasiliy Kulikov (segoon@openwall.com):
> As Yama's sysctls are about defining a security policy for the system,
> it is reasonable to define it per container in case of LXC containers
> (or out-of-tree alternatives like OpenVZ). In my opinion they belong
> to pid namespace. With per-pid_ns sysctls it is possible to create
> multiple containers with different ptrace, /tmp, etc. policies.
>
> The patch is straightforward:
>
> 1) all sysctl variables are moved from global vars to pid_namespace
> fields.
>
> 2) each cloned pid ns gets the settings of the parent.
>
> 3) the variables of current pid ns are visible through sysctl interface.
>
> proc_pid_dointvec_minmax() is stolen from its ipc_ns equivalent in
> ipc/ipc_sysctl.c.
>
> P.S. As user namespaces are not merged yet and it's not clear when/whether
> they are merged, these changes belong to pid namespace for now. When
> user namespaces are merged, per pid_ns variables should go to struct
> user_namespace. It will not break ABI as userspace sees the same
> kernel.yama.* sysctls in both pid ns and user ns cases.
>
> Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>

Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>

thanks,
-serge

> --
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 38d1032..46edaf8 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -30,6 +30,11 @@ struct pid_namespace {
> #ifdef CONFIG_BSD_PROCESS_ACCT
> struct bsd_acct_struct *bacct;
> #endif
> +#ifdef CONFIG_SECURITY_YAMA
> + int ptrace_scope;
> + int protected_sticky_symlinks;
> + int protected_nonaccess_hardlinks;
> +#endif
> };
>
> extern struct pid_namespace init_pid_ns;
> diff --git a/kernel/pid.c b/kernel/pid.c
> index fa5f722..0cd8926 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -78,6 +78,11 @@ struct pid_namespace init_pid_ns = {
> .last_pid = 0,
> .level = 0,
> .child_reaper = &init_task,
> +#ifdef CONFIG_SECURITY_YAMA
> + .ptrace_scope = 1,
> + .protected_sticky_symlinks = 1,
> + .protected_nonaccess_hardlinks = 1,
> +#endif
> };
> EXPORT_SYMBOL_GPL(init_pid_ns);
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index e9c9adc..73d47c4 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -101,6 +101,14 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
> if (err)
> goto out_put_parent_pid_ns;
>
> +#ifdef CONFIG_SECURITY_YAMA
> + ns->ptrace_scope = parent_pid_ns->ptrace_scope;
> + ns->protected_sticky_symlinks =
> + parent_pid_ns->protected_sticky_symlinks;
> + ns->protected_nonaccess_hardlinks =
> + parent_pid_ns->protected_nonaccess_hardlinks;
> +#endif
> +
> return ns;
>
> out_put_parent_pid_ns:
> diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
> index a92538c..cf99a8c 100644
> --- a/security/yama/yama_lsm.c
> +++ b/security/yama/yama_lsm.c
> @@ -16,10 +16,7 @@
> #include <linux/ptrace.h>
> #include <linux/prctl.h>
> #include <linux/ratelimit.h>
> -
> -static int ptrace_scope = 1;
> -static int protected_sticky_symlinks = 1;
> -static int protected_nonaccess_hardlinks = 1;
> +#include <linux/pid_namespace.h>
>
> /* describe a PTRACE relationship for potential exception */
> struct ptrace_relation {
> @@ -250,7 +247,7 @@ static int yama_ptrace_access_check(struct task_struct *child,
>
> /* require ptrace target be a child of ptracer on attach */
> if (mode == PTRACE_MODE_ATTACH &&
> - ptrace_scope &&
> + current->nsproxy->pid_ns->ptrace_scope &&
> !capable(CAP_SYS_PTRACE) &&
> !task_is_descendant(current, child) &&
> !ptracer_exception_found(current, child))
> @@ -292,7 +289,7 @@ static int yama_inode_follow_link(struct dentry *dentry,
> const struct inode *inode;
> const struct cred *cred;
>
> - if (!protected_sticky_symlinks)
> + if (!current->nsproxy->pid_ns->protected_sticky_symlinks)
> return 0;
>
> /* if inode isn't a symlink, don't try to evaluate blocking it */
> @@ -362,7 +359,7 @@ static int yama_path_link(struct dentry *old_dentry, struct path *new_dir,
> const int mode = inode->i_mode;
> const struct cred *cred = current_cred();
>
> - if (!protected_nonaccess_hardlinks)
> + if (!current->nsproxy->pid_ns->protected_nonaccess_hardlinks)
> return 0;
>
> if (cred->fsuid != inode->i_uid &&
> @@ -395,6 +392,26 @@ static struct security_operations yama_ops = {
> static int zero;
> static int one = 1;
>
> +static void *get_pid_data(ctl_table *table)
> +{
> + char *which = table->data;
> + struct pid_namespace *pid_ns = current->nsproxy->pid_ns;
> + which = (which - (char *)&init_pid_ns) + (char *)pid_ns;
> + return which;
> +}
> +
> +static int proc_pid_dointvec_minmax(ctl_table *table, int write,
> + void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> + struct ctl_table pid_table;
> +
> + memcpy(&pid_table, table, sizeof(pid_table));
> + pid_table.data = get_pid_data(table);
> +
> + return proc_dointvec_minmax(&pid_table, write, buffer, lenp, ppos);
> +}
> +
> +
> struct ctl_path yama_sysctl_path[] = {
> { .procname = "kernel", },
> { .procname = "yama", },
> @@ -404,28 +421,28 @@ struct ctl_path yama_sysctl_path[] = {
> static struct ctl_table yama_sysctl_table[] = {
> {
> .procname = "protected_sticky_symlinks",
> - .data = &protected_sticky_symlinks,
> + .data = &init_pid_ns.protected_sticky_symlinks,
> .maxlen = sizeof(int),
> .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> + .proc_handler = proc_pid_dointvec_minmax,
> .extra1 = &zero,
> .extra2 = &one,
> },
> {
> .procname = "protected_nonaccess_hardlinks",
> - .data = &protected_nonaccess_hardlinks,
> + .data = &init_pid_ns.protected_nonaccess_hardlinks,
> .maxlen = sizeof(int),
> .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> + .proc_handler = proc_pid_dointvec_minmax,
> .extra1 = &zero,
> .extra2 = &one,
> },
> {
> .procname = "ptrace_scope",
> - .data = &ptrace_scope,
> + .data = &init_pid_ns.ptrace_scope,
> .maxlen = sizeof(int),
> .mode = 0644,
> - .proc_handler = proc_dointvec_minmax,
> + .proc_handler = proc_pid_dointvec_minmax,
> .extra1 = &zero,
> .extra2 = &one,
> },
> ---


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